49ERS Not certain about quarterback Alex Smith

Ken Dorsey and Cody Pickett are the only backups for the 21-year-old rookie.
SANTA CLARA, Calif. (AP) -- Alex Smith sprained his right knee in San Francisco's fifth straight loss, and the 49ers aren't certain their rookie franchise quarterback will play against Tampa Bay on Sunday.
Smith, 8-of-16 for 92 yards and one interception in the Niners' humiliating 52-17 defeat, was hurt when his cleats got caught in the turf while LaVar Arrington tackled him in the first quarter.
He played the rest of the game, feeling only momentary pain -- but after his knee stiffened up overnight, the No. 1 overall draft pick wore a heavy wrap and a brace Monday at the 49ers' training complex.
Probable
He is listed as probable on the injury report, but the 49ers will wait until later in the week to determine whether Smith can make his third career start.
Smith sprained two ligaments on the inside of his knee, and fluid built up behind his kneecap. Though he had previous back injuries from weightlifting, he had never been hurt while playing football in high school or at Utah.
"I guess that's why I do things like that," Smith said, referring to his dangerous attempt to make a play while Arrington was bearing down on him. "Other people would have gone out of bounds or gone down. Obviously, I need to learn from that."
Last week, the 49ers traded Tim Rattay, Smith's veteran backup, to the Buccaneers for a low-round conditional draft pick. The move was meant to cement their faith in Smith while adding a ninth draft choice for next spring -- but it left Ken Dorsey and Cody Pickett as the only backups for a 21-year-old rookie whose head is still swimming at the speed of the NFL game.
Smith underwent an MRI exam Monday, and he'll have therapy and rehabilitation before practice on Wednesday.
"We've just got to see how much I can tolerate," he said.
Dismal season
The season has been equally rough for Smith and his teammates. The 49ers have fallen to 1-5 with dismal efforts on offense, defense and special teams -- but Smith's numbers are just as bad as you might expect from a rookie quarterback on a rebuilding team that had the NFL's worst record last season.
After two starts and two relief appearances in place of Rattay, Smith is 23-of-50 for 200 yards. He has thrown five interceptions and is still waiting for his first touchdown pass, leading to a quarterback rating of 17.5.